The first general staff specification for a flamethrowing tank was put forward as early as 1938, although at that time there was no research department dealing specifically with flame warfare. Some desultory trials led to a number of experimental models. but nothing definite was achieved until a special Petroleum Warfare Department was established, and then some more definite work was commenced. The PWD concentrated on a type of projector that used compressed hydrogen to propel the flame fuel jet, and in time this led to the Crocodile.

The Crocodile was meant to be used with the Churchill infantry tank, hence Churchill Crocodile. When it first appeared in 1942 a change of War Office policy meant that there was officially no longer a requirement for the flamethrower tank, but work nevertheless went ahead. It was just as well, for in April 1943 another policy change meant that the Crocodile was wanted once more and in August 1943 an order for 250 was placed, these vehicles being needed to equip units that would take part in the forthcoming Normandy landings.

The order was made despite the fact that no troop trials had taken place, Although the initial plan was that the Crocodiles were to be mounted on the Churchill Mk IV. most production weapons were installed in the Churchill Mk VII. The main part of the Crocodile was installed in a two-wheeled trailer towed behind the Churchill tank and connected to the tank via a universal joint through which the pressurized fuel had to pass. The projector itself was at the front of the tank. installed in place of the hull machine-gun. The Churchill's main 75-mm (2.95-in) gun and turret machine-gun were retained to enable the vehicle to be used as a normal gun tank if required. The trailer could be jettisoned when empty or if the occasion demanded. The trailer contained enough fuel and compressed gas to produce about 80 one second flame bursts, and the usual operational range was about 80 yards (73m), although under favourable conditions 120-yard (110m) range was possible.

The Churchill Crocodiles first went into action on D-Day, 6 June 1944. Thereafter they were used in all theatres of war and came to be very effective weapons that were greatly feared by the enemy. There were plans for Crocodiles to be used on Sherman tanks operated by the US Army and although some design work was carried out only six were built and of those only four were used in action by the Americans in Europe.

By the time the war ended 800 Churchill Crocodiles had been produced. The main British army user was the 79th Armoured Division, although other formations also had the type. Once the war was over most were withdrawn from use.